There are two general approaches to monitoring the pressure in vehicle tires: direct and indirect. Direct tire pressure monitoring systems (TPMS) typically comprise a wheel module having one or more sensors and electronics mounted in or to the tire to directly measure the tire's pressure and wirelessly transmit measurement data to the vehicle. Indirect TPMSs generally utilize information from other vehicle sensors and/or systems to indirectly estimate a tire's pressure without TPMS sensors or electronics being located in the tire. Indirect TPMS is attractive because it can be more cost-efficient than direct TPMS.
Many conventional indirect TPMS use wheel speed signals from the anti-lock brake system (ABS). For a typical passenger vehicle having four tires, the conventional indirect TPMS compares speed signals from each of the four wheels to determine whether an individual wheel is rotating faster because of a loss of pressure and related decreased in diameter of the tire. One drawback to this kind of indirect TPMS is that the systems cannot detect whether all wheels have lost pressure over time.
One approach for overcoming this drawback is to utilize a resonance frequency method (RFM) of analysis of a single resonance frequency in the sensed data signals from the ABS. U.S. Pat. Nos. 8,207,839 and 8,347,704 describe different kinds of RFM analysis of a time series of sensed data signals that includes auto-regression analysis, Fast Fourier analysis, a Bayesian analysis, or analysis based on a linear estimation model. While different kinds of analysis are taught by these patents, the purpose of each of these known RFM approaches is to reduce the amount of computation power required in an on-board processor to do the calculations necessary to identify a single resonance frequency from which tire pressure can be indirectly estimated.
While RFM analysis can represent an improvement over conventional indirect TPMS, the accuracy of the results can be impacted by the low resolution of the ABS sensed data signals and by other factors that can influence the resonance frequency beyond just the tire pressure in an individual tire. Therefore, there is a need for improved systems and methods for indirect tire pressure monitoring.